Abstract: An apparatus for safeguarding a welding pool in mechanized welding in a constrained position, for example a vertical position, comprises sliding blocks pressed against the surfaces of the work pieces to be welded and supplying the welding current and the welding electrode and moving at the welding rate. The sliding blocks comprise two segments which are closely adjacent in the perpendicular center plane of the welding gap between the work pieces and are mutually movable. The sliding block segments are pressed in a yielding manner against the surface of each work piece and are individually and independently movable.